1. Field of the Invention
The present invention relates to a novolak resin solution, a positive photoresist composition, and a method of producing the same.
2. Description of the Related Art
Photoresists comprising an alkali soluble resin and a quinonediazide group containing compound display excellent resolution, sensitivity, etching resistance and heat resistance in photolithography techniques utilizing i-line radiation (365 nm), and are consequently widely used in the production of semiconductor elements and liquid crystal elements.
However, positive photoresist compositions comprising an alkali soluble resin, typified by novolak resins, and a quinonediazide group containing compound typified by quinonediazide ester compounds may deteriorate over time following production, leading to variations in the resist characteristics such as the sensitivity and the resolution. In order to prevent this type of deterioration over time, various corrective actions are taken, including adding deterioration prevention agents, and storing the prepared resist composition in a cold, dark place, under an inert atmosphere.
Furthermore, Japanese Unexamined Patent Application, First Publication No. Hei 7-248619 discloses a positive photoresist composition with excellent storage stability and resistance to the formation over time of foreign matter, which is produced by adding an acidic compound such as p-toluenesulfonic acid or acetic acid to a resist composition.
In addition, Japanese Unexamined Patent Application, First Publication No. Hei 10-232489 discloses a method of preventing variations in the quality of a resist composition resulting from reduction of the quinonediazide type photosensitizer by adding a reduction prevention agent such as benzoquinone or naphthoquinone to the resist composition.
However, when investigated by the inventors of the present invention, it became evident that variations in the quality of resist compositions to which the methods of either Japanese Unexamined Patent Application, First Publication No. Hei 7-248619 or Japanese Unexamined Patent Application, First Publication No. Hei 10-232489 had been applied, could not always be prevented. In other words, it was clear that even for a single product, fluctuations could occur in the characteristics of the product between production lots.